Referring to FIG. 1 of the drawings, reference numeral 100 generally designates a vehicle that employs an anti-lock braking system. Vehicle 100 generally comprises wheels 102-1 to 102-4, wheel speed sensors (WSS) 104-1 to 104-4 (which are each associated with wheels 102-1 to 102-4, respectively), a mixed signal circuit (MSC) 106, and a microcontroller (MCU) 108. In operation, the MSC 106 provides power to each of the WSSs 104-1 to 104-2 through power cables (which can measure in the tens of feet), and the WSSs 104-1 to 104-2 provide data regarding wheel speed, direction, and so forth to MSC 106, which decodes the data for processing by MCU 106.
As a result of the complexity of wiring harnesses in vehicles (namely, the sheer volume of wires in the wiring harnesses), there is a desire to reduce the number of wires, which is the case with WSSs 102-1 to 102-4. As can be seen in FIG. 2, communications between WSS 102-1 (for example) and MSC 106 is performed through a power cable (which generally comprises a power wire PWR, a ground wire GND, and a capacitor C). Generally, each of the power wire PWR and ground wire GND is coupled to power and ground terminals (respectively) of each of the WSS 102-1 and MSC 106). Because the power wire PWR serves multiple purposes (i.e., providing power and communications), the communication of data is performed through the use of current-domain signals.
Turning to FIG. 3, an example of these current-domain communication signals can be seen. To transmit data corresponding to wheel speed and other information, the current-domain signals (which are Manchester encoded) use multiple current levels. For example, for wheel speed data, current levels between 14 mA and 28 mA are employed, while other encoded data may use current levels between 7 mA and 14 mA. As can be seen from FIG. 3, however, the noisy environment of a vehicle (as well as noise reducing elements, like capacitor C) can severely degrade these current-domain signals, resulting in errors in determining the actual pulse width of a wheel speed pulse, which affect time base measurements.
Therefore, there is a need for an improved measurement system and method.
Another conventional system is: U.S. Pat. No. 5,149,177.